A Lucid key is designed to use a combination of character states and visual cues; after selecting one or several character states the remaining candidate species can be examined with illustrations and photos. From there, the user can opt to either put in more character states to further narrow the list or visually examine the remaining candidate species and exclude them one-by-one. This is especially useful when the distinguishing characters are difficult to capture in discrete terms, such as patterns on the wings, scutum, and abdomen.
Never assume that you will always end up with just one entity remaining. Some entities in the key may be very hard to differentiate, except when using difficult or obscure features. Sometimes, after you have addressed all the features, you may have a short list of entities remaining instead of just one entity. You are still much closer to an identification than you otherwise would have been. You may then have to refer to more advanced or specialist reference sources, including DNA sequence data. Also keep in mind that the taxonomy of Dacini is only partly known, and it is possible that you are trying to identify a species that is yet unknown to science and not included in the key.
Without prior experience, the most efficient way to use the Lucid key is with the "Best" button indicated with a magic wand icon. It will jump to the most distinguishing character—i.e., a character that will remove (as close as possible to) 50% of the remaining species. For Dacini, the first character this option selects is the costal band, which is an excellent starting point. For all characters, when in doubt, it is possible to select multiple states. If you are completely unsure, skip the character altogether and use the best button again to go to the next best. During testing we determined that in most cases a species-level identification can be reached in seven steps or less.
"Spot" characters work the opposite way of the "best" button; they are features that are unique to one or a small set of species and quickly narrow down the selection of candidate species for the most efficient use of the key. This method uses prior knowledge of which character states are highly unusual and exclude more species at each step. Recognizing spot characters will happen from using the key frequently, and they are indicated on the species fact sheets. Examples of such character states for Dacini include dark markings on the scutellum, bands on the wings in addition to the costal band and anal streak, an elongated wasp-like abdomen, dark markings on the abdomen that do not form the typical dorsalis-like 'T'-pattern, and setae on the postpronotal lobes. The term "spot characters" (technical term: apomorphy) was coined by botanist Max van Balgooy for the Flora Malesiana (van Balgooy 1997van Balgooy 1997:
van Balgooy, Max MJ, 1997. "Spot-characters. An aid for identification of families and genera." Malesian seed plants-an aid or identification of families and genera 1, no. 1 (1997): 1–154.) and has proven very useful for obtaining identifications when there are many candidate species.
The scientific illustrations capture the majority of the relevant characters for identification in a single image but are not yet available for all species. When species are variable for certain characters, the illustration depicts the most common form across the entire species' distribution. However, some forms can be regionally more common. The photo plates are available for most species and include multiple views to capture the relevant characters, but character states can be more difficult to assess in these due to artifacts from the preservation process (e.g., wrinkled wings or curled up abdomens). The colors can also appear different between dried specimens and specimens preserved in ethanol; more faded in the former and more vibrant in the latter. The colors in the illustrations aim to resemble those of live specimens.
The Adult Bactrocera fruit fly ID website has a keyword search option that will look for a query term across the website, but not within the Lucid key. To search within the Lucid key, use the magnifying glass button in the key's toolbar. This will search for a term within the selected quadrant only. If, for example, you select the "entities remaining quadrant" (highlighted in blue when selected, grey when not), you can search for a specific species, subgenus, or genus.
Authors: Doorenweerd et al.
Last updated April 2025
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